Photographic silver halide diffusion transfer process



United States Patent PHOTOGRAPHIC SILVER HALIDE DIFFUSION TRANSFER PROCESS Denis James Goodchild and John Derek Knowles, Wealdstone, England, assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed May 4, 1959, Ser. No. 810,576

7 Claims. (CI. 96-29) This invention relates to photographic processes for producing direct positive images and to materials for use therein.

In photography, most of the layers in which photographic images are found are themselves originally lightsensitive. However, not all photographic layers used for forming images are light-sensitive and the present invention concerns a class of non-light-sensitive layers, namely, those containing silver precipitating agents such as physical development nuclei for silver salts, e.g. collodial silver or silver sulfide, or a chemical precipitant for silver ions, e.g. zinc sulfide. Such non-light-sensitive layers are used to form positive silver or silver salt images therein by reaction between the substances in the layers and dissolved silver salts diffusing image-wise thereinto from a contiguous silver halide emulsion layer which has been exposed image-wise and which has been or is being developed to a negative image.

One drawback sometimes encountered in processes of this type is that the positive image produced is of a brownish or other non-acceptable colour.

The present invention provides a sheet material comprising a non-light-sensitive photographic layer contain ing a silver precipitating agent such as mentioned and also containing a mercaptotetrazaindene.

The invention includes the process of preparing a direct positive image which comp-rises exposing a photographic silver halide emulsion layer to an object or image, developing a negative image in the exposed layer, and, during or after development, transferring silver halide from the unexposed areas of the emulsion layer to a non-light-sensitive image-receiving layer containing the silver precipitating agent in effective contact with the emulsion layer, the transfer being effected in the presence of a silver halide solvent and a mercaptotetrazaindene.

By in effective contact we mean that dissolved silver salts can diffuse from the emulsion layer to the non-lightsensitve layer. There may be an intermediate layer present between the two aforesaid layers which does not hinder the silver salt diffusion, and the two layers may or may not be coated on the same support.

We have found that the presence of the tetrazaindene in many cases has the effect of producing a blacker positive image than would otherwise be produced.

In the process of the invention the tetrazaindene may be present in the receiving layer or in the solution employed for effecting development in the emulsion layer, or it may have been incorporated in the emulsion layer before exposure.

An alkaline solution is used to effect development of the exposed layer and the developing agent may be present in either the emulsion layer or in the alkaline solution or both. A mixture of developing agents may be used, if desired.

The silver halide solvent may be present in the developing solution or the receiving layer and is preferably sodium thiosulphate.

It is preferable to employ an antifoggant to prevent the formation of fog in the exposed emulsion layer and this may be present in either the emulsion layer or in the alkaline solution used to effect development. Any of the well-known nitrogen-containing organic antifoggants ice may be used and it has been found that benzotriazoles are very suitable.

Suitable tetrazaindenes which may be employed in the present invention are 1:2:3az4-tetrazaindenes and 1:3: 3a:7-tetrazaindenes. For the strongest effect, it is preferred to employ 1:3:3az7-tetrazaindenes substituted in the 2- or 4-position by a mercapto or substituted mercapto group and in the 5- or 6-positi0n by a lower alkyl group. It should be noted that the use of a 1:3:3az7- tetrazaindene substituted in the 5- or 6-position by an aryl group is usually found to have a detrimental effect on the transfer.

When employed in the receiving layer the tetrazaindenes are preferably incroporated in an amount of between 2 and 20 mgs./ sq. ft. such as about 5 mgs./ sq. ft.

The following compounds are representative of those suitable for use in the present invention.

011 NLOHI 2: G-dimethyl-l :3 3a: 7 -tetrazaindene-4-thiol SNa Js j Sodium salt of 6-methyl-l:3:3a:7-tetrazaindene-4-thiol.

2 methylmercapto 4 hydroxy 6 methyl 1 1:3:3a:7- tetrazaindene.

5 -methy1-1 :2: 3az4-tetrazaindenee7-thiol.

5-ethyl-6-methyl-1 :3 3a: 7-tetrazaindene 4-thiol.

5-bromo-6-methyl-1 :3 3a: 7-tetrazaindene-4-thiol.

There tetrazaindenes can be described as comprising a diazine ring fused to a triazole ring so that said rings have a single nitrogen atom in common and have a thiol substituent attached to a carbon atom of the diazine ring.

The preparation of the above hydroxy compound is described in Fry US. Patent 2,566,659 granted September 4, 1951, and the synthesis of the other compounds is described in the Knott US. patent application Serial No. 687,864, filed October 3, 1957, now US. Patent 2,933,388 granted April 19, 1960. These references provide other mercaptotetrazaindenes useful for the formation of neutral-tone images in the silver halide diffusion transfer processes of the invention.

A suitable non-light-sensitive layer for use in the present invention comprises a hydrophilic organic colloid layer, such as a gelatin layer, containing a silver precipitating agent of the nature described and also containing one of the tetrazaindenes of the invention.

Such a layer may be coated on a paper support and contacted with an exposed and developing emulsion layer coated on a separate support in the presence of a silver halide solvent, or may be coated on the same support as the emulsion layer. In the latter case, it is preferable to coat the non-light-sensitive layer on a paper support, then to overcoat this layer with a comparatively unhardened emulsion layer or other emulsion layer of different solubility such as a cellulose ether phthalate emulsion. After exposure, development and formation of the direct positive image in the non-light-sensitive layer, the exposed and developed unhardened emulsion layer is removed, for example by Washing in warm water.

The following example illustrates the present invention.

Exam'ple A high contrast silver chloride emulsion containing the following constitutents is coated on a paper support at the mentioned coating rate.

Grams/ sq. m.

Silver chloride 1.4 Diphenyl iodonium S-methyl benztriazole 0.063 Hydroquinone 0.28 Gelatin- 5.6

The resulting emulsion layer is exposed to a subject such as document and treated by the following developer:

. Grams Sodium sulphite (anh.) 75 Hydroquinone 18 Sodium hydroxide 11.5 1-phenyl-3-pyrazolidone 0.5

Water to 1 litre.

Gelatin 6.2 Sodium thiosulphate (anh.) 1.4 Titanium dioxide 0.63

Silver sulphide 0.004 2:6-dimethyl-1 :3 :3az7-tetrazaindene-4-thiol 0.05

After separating the layer and the sheet, a positive image of a good black colour was obtained on the receiving sheet.

The other tetrazaindenes may be used in the receiving layer or in the developer composition for the process in a similar manner. The photographic emulsions containing the mercapto-tetrazaindene compounds prepared in the manner disclosed in the mentioned invention of Knott may also be used in the silver halide diffusion transfer processes of the present invention with the result that development of the emulsion layers with developer compositions of the nature described containing silver halide solvent and in contact with a nucleated reception layer results in the transfer of the undeveloped silver halide to the reception layer and the formation therein of a silvereontaining image of neutral tone.

The tetrazaindenes can be used in a similar manner in a sensitive multilayer element of the type described in the Yackel et al. US. patent application Serial No. 586,705 filed May 23, 1956, wherein a unitary element is provided having on a support a reception layer containing a silver precipitant such as colloidal silver and if desired, silver halide solvent, and coated thereover a removable cellulose ether phthalate silver halide emulsion layer. In this element the tetrazaindene compounds of the invention may be dispersed in the reception layer, the overlying emulsion layer or may be contained in the developing solutions. On development of the sensitive element with a developer composition, such as shown above, containing silver halide solvent, if the latter is not present in the sensitive element, the positive undeveloped silver halide transfers to the reception layer and forms a neutral-colored silver-containing image under the influence of the tetra zaindene present during the transfer step. Subsequently the emulsion layer which has become solubilized by the developer alkali can be gently rubbed oif leaving a neutral-colored positive image on the support.

Additional well-known silver precipitating agents useful in the sensitive elements of the invention are described in the above invention of Yackel et al.

As used herein, mercapto includes not only -SH, --S alkyl, but also water soluble salts thereof such as sodium ammonium or organic amine etc. salts.

What we claim is:

l. A process for preparing a photographic image of improved tone which comprises exposing a photographic silver halide emulsion layer to a subject, developing the emulsion layer, transferring the silver halide from the undeveloped areas of the emulsion layer to an imagereceiving layer containing a silver precipitating agent, the transfer being effected in the presence of a silver halide solvent and a mercaptotetrazaindene substituted in at least one of the 5 and 6 nuclear positions only by a substituent of the class consisting of lower alkyl groups.

2. The process of claim 1 wherein the mercaptotetrazaindene is persent in the imagereceiving layer together with the silver precipitating agent.

3. A process for preparing a photographic image of the improved tone which comprises exposing a photographic silver halide emulsion layer to a subject, developing the emulsion layer, transferring the silver halide from the undeveloped areas of the emulsion layer to an image-receiving layer containing a silver precipitating agent, the transfor being effected in the presence of a silver halide solvent and a mercapto l,2,3a,4-tetrazaindene substituted in at least one of the 5 and 6 nuclear positions only by a sub stituent of the class consisting of lower alkyl groups.

4. A process for preparing a photographic image of improved tone which comprises exposing a photographic silver halide emulsion layer to a subject, developing the emulsion layer, transferring the silver halide from the undeveloped areas of the emulsion layer to an image-receiving layer containing a silver precipitating agent and 2,6-dimethyl-1,3,3a,7-tetrazaindene-4-thiol, the transfer being etfected in the presence of a silver halide solvent.

5. A process for preparing a photographic image of improved tone which comprises exposing a photographic silver halide emulsion layer to a subject, developing the emulsion layer, transferring the silver halide from the undeveloped areas of the emulsion layer to an image-receiving layer containing a silver precipitating agent and 6-methyl-l,3,3a,7tetrazaindene-4-thiol, the transfer being effected in the presence of a silver halide solvent.

6. A process for preparing a photographic image of improved tone which comprises exposing a photographic silver halide emulsion layer to a subject, developing the emulsion layer, transferring the silver halide from the undeveloped areas of the emulsion layer to an image-receiving layer containing a silver precipitating agent and 2 methylmercapto 4 hydroxy 6 methyl 1,3,3a,7- tetrazaindene, the transfer being effected in the presence of a silver halide solvent.

7. A process for preparing a photographic image of improved tone which comprises exposing a photographic silver halide emulsion layer to a subject, developing the emulsion layer, transferring the silver halide from the undeveloped areas of the emulsion layer to an image-receiv- 5 6 ing layer containing a silver precipitating agent and 2,704,721 Land Mar. 22, 1955 S-methyl-1,2,3a,4-tetraZaindene-7-thio1. 2,835,581 Tinker May 20, 1958 2,933,388 Knott Apr. 19, 1960 References Cited in the file of this patent 2,000,736 Karlson Sept. 19, 1961 UNITED STATES PATENTS 5 FOREIGN PATENTS 2,352,014 Rott June 20, 1944 783,793 Great Britain Oct. 2, 1957 

1. A PROCESS FOR PREPARING A PHOTOGRAPHIC IMAGE OF IMPORVED TONE COMPRISES EXPOSING A PHOTOGRAPHIC SILVER HALIDE EMULSION LAYER TO A SUBJECT, DEVELOPING THE EMULSION LAYER, TRANSFERRING THE SILVER HALIDE FROM THE UNDEVELOPED AREAS OF THE EMULSION LAYER TO AN IMAGERECEIVING LAYERS CONTAINING A SILVER PRECIPITATING AGENT, THE TRANSFER BEING EFFECTED IN THE PRESENCE OF A SILVER HALIDE SOLVENT AND A MERCAPATOTETRAZAINDENE SUBSTITUED IN AT LEAST ONE OF THE 5 AND 6 NUCLEAR POSITION ONLY BY A SUBSTITUENT OF THE CLASS CONSISTING OF LOWER ALKYL GROUPS. 